Modulation and coding course- lecture 3

Transforming the information source to a form compatible with a digital system-Sampling-Aliasing-Quantization-Uniform and non-uniform-Baseband modulation-Binary pulse modulation-M-ary pulse modulation-M-PAM (M-ay Pulse amplitude modulation)
Nội dung trích xuất từ tài liệu:
Modulation and coding course- lecture 3Digital Communication I:Modulation and Coding Course Period 3 - 2007 Catharina Logothetis Lecture 3Last time we talked about: Transforming the information source to a form compatible with a digital system Sampling Aliasing Quantization Uniform and non-uniform Baseband modulation Binary pulse modulation M-ary pulse modulation M-PAM (M-ay Pulse amplitude modulation) Lecture 3 2 Formatting and transmission of baseband signal Digital info. Bit stream Pulse waveforms (Data bits) (baseband signals) Textual Formatsource info. Pulse Analog Sample Quantize Encode modulate info. Sampling at rate Encoding each q. value to f s = 1 / Ts l = log 2 L bits (sampling time=Ts) (Data bit duration Tb=Ts/l) Quantizing each sampled Mapping every m = log 2 M data bits to a value to one of the symbol out of M symbols and transmitting L levels in quantizer. a baseband waveform with duration T Information (data) rate: Rb = 1 / Tb [bits/sec] Symbol rate : R = 1 / T [symbols/sec] For real time transmission: Rb = mR Lecture 3 3 Quantization example amplitude x(t) 111 3.1867 110 2.2762 Quant. levels 101 1.3657 100 0.4552 011 -0.4552 boundaries 010 -1.3657 001 -2.2762 x(nTs): sampled values xq(nTs): quantized values 000 -3.1867 Ts: sampling time PCM tcodeword 110 110 111 110 100 010 011 100 100 011 PCM sequence Lecture 3 4Example of M-ary PAMAssuming real time tr. and equal energy per tr. data bit forbinary-PAM and 4-ary PAM: • 4-ary: T=2Tb and Binay: T=Tb • A2 = 10B 2 Binary PAM 4-ary PAM (rectangular pulse) (rectangular pulse) 3B A. ‘11’ ‘1’ B T T T ‘01’ T -B ‘00’ T T ‘0’ ‘10’ -A. -3B Lecture 3 5Example of M-ary PAM …0 Ts 2Ts 2.2762 V 1.3657 V0 Tb 2Tb 3Tb 4Tb 5Tb 6Tb 1 1 0 1 0 1 Rb=1/Tb=3/Ts R=1/T=1/Tb=3/Ts0 T 2T 3T 4T 5T 6T Rb=1/Tb=3/Ts R=1/T=1/2Tb=3/2Ts=1.5/Ts0 T 2T 3T Lecture 3 6Today we are going to talk about: Receiver structure Demodulation (and sampling) Detection First step for designing the receiver Matched filter receiver Correlator receiver Lecture 3 7Demodulation and detection mi Pulse g i (t ) Bandpass si (t ) M-ary modulation Format modulate modulate i = 1, K, M channel transmitted symbol hc (t ) estimated symbol n(t ) Demod. Format Detect ˆ mi z (T ) & sample r (t )Major sources of errors: Thermal noise (AWGN) disturbs the signal in an additive fashion (Additive) has flat spectral density for all frequencies of interest (White) is modeled by Gaussian random process (Gaussian Noise) Inter-Symbol Interference (ISI) ...